It is well known in the art that the amplitude of a sound produced by a piano, a representative example of manually operated key-type musical instruments, is inversely proportional to the square value of the key-fly state of a key. Skilled pianists utilize this property of pianos ingeniously and adjust not only the pitches but the volumes of sounds by depressing keys with controlled finger pressures to produce subtle sounds. The term "key-fly" state as above mentioned refers to the period of time for which a key is being depressed, viz., a key is in a state flying from a key-off state released from finger pressure toward a fully-depressed or key-on state under a pressure manually applied to the key.
Electronically operated key-type musical instruments are presently in use and are expected to have potential expressibilities comparable to those of traditional pianos. Such electronic instruments are also required to be capable of producing sounds in volumes which vary in certain relationships to key-fly states. To meet such a requirement, a known electronically operated key-type musical instrument has incorporated therein a control device including key-touch sensors. The key-touch sensors are provided respectively in association with the individual keys of the instrument and are adapted to produce analog signals, or voltages, which vary in a particulate functional relationship with the periods of time for which the keys are in the key-fly states.
The signal voltages thus produced by the key-touch sensors are stored in capacitors which are also provided respectively in association with the individual keys of the instrument. Provision of such a large number of capacitors results in added intrication of the instrument and accordingly in deterioration of the performance reliability and an increase in the production cost of the instrument. The key-touch sensors being electrically connected to the keys by wires respectively intervening therebetween, disproportionately large amounts of time and labor are further required for the wiring and adjustment of the sensors and the associated elements.
Attempts have thus far been made to provide solutions to these problems inherent in electronically operated key-type instruments of the described type, one of which attempts is disclosed in Japanese Provisional Patent Publication No. 56-161594. In this published material is disclosed a sound-volume control device using a single key-touch counter common to all of the keys of the instrument. The single key-touch counter is assigned in time sharing to the individual keys of the instrument and counts the duration of the fly-state of each of the keys depressed to indicate the detected duration in the form of digital signals. The counting of the durations of key-fly states is effected only during the elementary cycles of operation of each machine cycle of a key assigner when the bus line is maintained out of use.
A control device of this nature still has a drawback in that the key-touch counter must be arranged with extra retrieval means to convert the results of the counting into appropriate key-touch values which vary with the counts.
An object of the present invention is to provide a key-touch value control device which is constructed and arranged so that key touch values are calculated in such a manner as to follow a characteristic curve which can be modified by modifying the configuration of operation command data and that such calculation is executed on a real time basis during the periods of time for which keys are being depressed. The operation command data can thus be modified without monitoring the periods of time for which keys are being depressed and, for this reason, the key-touch value control device can be constructed compactly since no such means need be provided that would otherwise be required for monitoring the durations of key-fly states and converting the resultant signals into key-touch values to follow a desired characteristic curve.